The invention relates to a process for heating the passenger compartments of motor vehicles by means of the waste heat given off by the engine via the liquid or gaseous coolant, which is fed back to the engine through coolant lines via a passenger compartment heat exchanger in order to heat the passenger compartment, and a device for implementing the process.
Against the backdrop of constant improvements in the efficiency of combustion engines, drive technology and aerodynamics in motor vehicle construction, simple thermodynamic considerations quickly make it apparent that considerably more efficient methods must be developed in future for utilising the waste heat given off by the engine for heating purposes, particularly for heating the passenger compartment.
Depending on the efficiency and the driving situation, vehicles with highly efficient diesel engines already on the market today display problems with heating the passenger compartment under extreme climatic conditions: in addition to the very slow heating-up of the engine and the passenger compartment, the heating capacity while driving at low loads is often insufficient to achieve a comfortable climate in the passenger compartment, even after a relatively long journey.
Therefore, some motor vehicle manufacturers are trying to eliminate this heating capacity deficit by means of an additional, fuel-fired or electrically heated heat source, as sufficient heating capacity for the passenger compartment could not be provided by optimising the coolant system alone. This is not surprising at first glance, as the coolant/heating systems currently on the market are already the product of many years' optimisation involving variation of the coolant, fresh-air and circulating-air mass flows, as well as the geometry and position of the passenger compartment heat exchangers and control valves.
Furthermore, the loss of heat to the surrounding environment can, for example, be reduced by thermal encapsulation of the engine, improvement of the insulation of the passenger compartment, recovery of heat from the exhaust gas, an increase in the circulating air mass flow in the passenger compartment or even by recovery of the heat still contained in the air escaping from the passenger compartment into the surrounding environment via a waste-air/fresh-air heat exchanger, meaning that the use of additional heating systems or heating energy can be at least partly dispensed with.
However, these measures entail considerable additional costs, which renders them unattractive, particularly for smaller vehicles. That said, precisely this class of vehicles in conjunction with highly efficient engines already has very low fuel consumption and thus also little waste heat for heating purposes as a result of their low mass.
The invention is based on the task of creating an efficient and low-cost process for reducing the loss of heat to the surrounding environment for motor vehicles with coolant-heated passenger compartments, so that as little additional heating energy as possible is needed to heat the passenger compartment. At the same time, the heating-up time of the engine is to be reduced and undercooling of the engine when stationary avoided as far as possible, with modifications to existing vehicle components being kept to a minimum.
Furthermore, a device for implementing the process is to be created which is to be as simple and inexpensive as possible to manufacture and use.